1. Field of the Invention
The present invention relates to a fluid pressure device such as a flow control valve for controlling a supply amount of pressurized fluid.
2. Description of the Related Art
A control valve as one example of the fluid pressure device includes a valve housing, and a spool movably mounted in the valve housing, as well as an introducing hole and a discharging hole both formed in the valve housing. The spool is provided with a cylindrical spool portion, the valve housing is formed with a cylindrical hole, and the spool portion is movably inserted in the cylindrical hole in its axial direction. In such a control valve, if the spool is moved, the introducing hole and the discharging hole are brought into communication as desired, thereby discharging pressurized fluid, e.g., pressurized oil from the introducing hole outside from the discharging hole.
In the case of this kind of control valve, a fluid groove is formed in an outer peripheral surface of the spool portion. The fluid groove is formed into a ring-like shape, and one or more fluid grooves are provided in the axial direction of the spool portion. By providing the fluid grooves in this manner, the pressurized fluid held in the fluid grooves substantially uniformly act on the entire region of the spool portion in its peripheral direction so that the pressure of the pressurized fluid acting in the peripheral direction can be uniformed.
When the plurality of fluid grooves are provided in the spool portion in this manner, if the spool portion of the spool is located concentrically with the cylindrical hole of the valve housing, an annular gap is generated between an outer peripheral surface of the spool portion and an inner peripheral surface of the cylindrical hole, and the pressurized fluid flows through the annular gap. Therefore, substantially uniform fluid pressure acts on the spool portion in its peripheral direction. However, if the spool portion is deviated toward the inner side of the cylindrical hole, and a part of the spool portion contacts with the cylindrical hole, and if only a side of the spool portion on which the pressurized fluid is acting due to uneven manufacturing precision or inclination of the spool portion, the fluid pressure does not act on a side of the spool portion which receives lower pressure, and the part of the spool portion is pushed against the inner peripheral surface of the cylindrical hole. When such a contacting state is generated, a great force is required to move the spool portion, and it is difficult to smoothly move the spool.
Such a problem exists in general fluid pressure devices in which the cylindrical spool portion is movably inserted into the cylindrical hole of the housing.
In a fluid pressure device having no fluid groove, it is generally known to increase the size of the gap of the shaft seal portion receiving high pressure. However, when this is constituted only by the seal portion, if the shaft is moved in its axial direction, the initially set relation of gap is changed, there are problems that a sufficient sealing performance can not be obtained, a sufficient force for keeping the shaft concentrically, and the like.
It is an object of the present invention, to provide a fluid pressure device in which a cylindrical spool portion of a shaft member is concentrically held in a cylindrical hole of a housing, and the cylindrical spool portion can be moved smoothly.